Nginw + FastCGIwrap = 502 bad gateway

[Otyugh]

Greetings,

I'm trying to get a C compiled program to work using fcgi with nginx, but I'm showed a 502 Bad Gateway.
The actual setup is : all programs in ./cgi-bin/*.cgi should use fcgiwarp. The actual result is every adress matching report 502 Bad Gateway.

I'm not sure of what I am missing :s

>sudo service fcgiwrap status
[ ok ] Checking status of FastCGI wrapper: fcgiwrap running.

>sudo netstat -anp | grep cgi
unix  2      [ ACC ]     STREAM     LISTENING     12743    4055/fcgiwrap       /var/run/fcgiwrap.socket


relevant extract of /etc/nginx/sites-available/blog 
	location ~ ^/cgi-bin/.*\.cgi$ {
	  # Disable gzip (it makes scripts feel slower since they have to complete
	  # before getting gzipped)
	  gzip off;

	  # Set the root to /usr/lib (inside this location this means that we are
	  # giving access to the files under /usr/lib/cgi-bin)
	  root  /usr/lib;

	  # Fastcgi socket
	  fastcgi_pass  unix:/var/run/fcgiwrap.socket;

	  # Fastcgi parameters, include the standard ones
	  include /etc/nginx/fastcgi_params;

	  # Adjust non standard parameters (SCRIPT_FILENAME)
	  fastcgi_param SCRIPT_FILENAME  /usr/lib$fastcgi_script_name;
	}

>tail -n 2 /var/log/nginx/error.log
2014/09/02 14:28:16 [error] 4324#0: *13 upstream prematurely closed FastCGI stdout while reading response header from upstream, client: 127.0.0.1, server: notyugh.pwnz.org, request: "GET /cgi-bin/helloworld.cgi HTTP/1.1", upstream: "fastcgi://unix:/var/run/fcgiwrap.socket:", host: "localhost"
2014/09/02 14:28:27 [error] 4324#0: *13 upstream prematurely closed FastCGI stdout while reading response header from upstream, client: 127.0.0.1, server: notyugh.pwnz.org, request: "GET /cgi-bin/FILEDONTEXIST.cgi HTTP/1.1", upstream: "fastcgi://unix:/var/run/fcgiwrap.socket:", host: "localhost"

More info :
> nginx -V
nginx version: nginx/1.2.1
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log --http-client-body-temp-path=/var/lib/nginx/body --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-log-path=/var/log/nginx/access.log --http-proxy-temp-path=/var/lib/nginx/proxy --lock-path=/var/lock/nginx.lock --pid-path=/var/run/nginx.pid --with-pcre-jit --with-http_gzip_static_module
--with-http_ssl_module --with-ipv6 --without-http_browser_module --without-http_geo_module --without-http_limit_req_module --without-http_limit_zone_module --without-http_memcached_module --without-http_referer_module --without-http_scgi_module --without-http_split_clients_module --with-http_stub_status_module --without-http_ssi_module --without-http_userid_module --without-http_uwsgi_module
--add-module=/build/nginx-n55HQd/nginx-1.2.1/debian/modules/nginx-echo

> dpkg -l | grep cgi
ii  fcgiwrap                              1.0.3-3                            armhf        simple server to run CGI applications over FastCGI
ii  libfcgi0ldbl                          2.4.0-8.1                          armhf        Shared library of FastCGI
ii  php5-cgi                              5.4.4-14+deb7u14                   armhf        server-side, HTML-embedded scripting language (CGI binary)
ii  spawn-fcgi                            1.6.3-1                            armhf        A fastcgi process spawner

> uname -a
Linux armServ 3.4.67+ #1 SMP PREEMPT Tue Dec 17 20:45:43 CET 2013 armv7l GNU/Linux